1. Field of the Invention
This invention relates to a volume controlling device for a variable volume pump, especially this invention has a special usage for using as an automotive power steering device. The amount of fluid discharged from the present pump changes as the fluid needs of the power steering device change.
2. Description of the Prior Art
Many kinds of volume controlling devices have been proposed, especially which vary pump volume while maintaining good pump efficiency. For example, the device described in Japanese patent KOKAI (laid-open publication), 58-110881 maintains the product of the output pressure and amount of fluid discharged constant while the device varies the pump volume in order to maintain pumping efficiency.
This conventional device, however, needs a special choke located in a special controlling channel. This controlling channel is different from the main channel through which the discharged fluid from the pump passes. Thus, the special choke needs the special controlling channel. Furthermore, the special choke needs working fluid for signaling. Since the special working fluid for the special choke should increase in relation with the amount of the discharged fluid, the special choke has the problem for wasting pump energy.